TBS Caipirinha 2 proper FC Setup

Hello. For those that are familiar with the TBS Caipirinha 2 wing, the flight controller is located away from the CG in a compartment inside one of the sides of the wing. This is a first for me since we always locate the FC to the center of the plane. From what I’ve read, I’m gathering I can use the IMU Pos offsets parameter to compensate for this? If so, can anyone provide a little more insight on the parameters? Do I apply a negative value to offset to the left side and positive to the right? I would appreciate anyone’s guidance on this topic. Particularly, if anyone’s built this same wing with Arduplane, I’d love to hear your thoughts on how you accomplished the setup. Thank you I advance for your assistance.

see https://ardupilot.org/plane/docs/common-sensor-offset-compensation.html for reference. imho the note at the article’s top sums it up pretty well. defaults generally are a good place to start from. there might be room for minuscule optimization by tuning the above mentioned offsets, most likely well below real-life perception threshold though.
once you’ve got your caipi dialed in well based on defaults and gathered some flightlogs, you might opt to adjust the offsets and see if you can spot any noticeable effect. i personally never got there though…

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Thank you @vierfuffzig for taking the time and interest in responding. I greatly appreciate it. The info provided is helpful. If I understand correctly, the default IMU offsets (not modifying any offsets) should still compensate for the offset from the center of the craft. Is this a correct assessment? I gather you have set up your Caipi 2 in the same fashion and have had success? From what I read, I’m gathering ArduPlane pretty much compensates for about 15cm offsets within its defaults. Any PIDs I should be considering? Thanks again

i personally have never actually owned or built a caipi2 :wink: but what i have done is successfully built and flown a dozen of airframes of various types, including wings in all kinds of size ranges, equipped with flightcontrollers running ardupilot, placed all over those airframes. plus, due to my affinity to the ardupilot environment, assisted in quite a few actual caipi2 fpv-type builds, most essentially the respective ardupilot FC setups.

afaik, the recommendation to keep your flight controller as close to cg as possible is a rule of thumb originally designed to avoid inherent accelerometer noise in multirotors, and it’s meant to be read within the limits of practicability.

however, looking at a traditional airplane’s flight physics, the way arduplane integrates available sensors’ data to acquire a position estimate and the actual amount of physical offset you will get when placing the controller into one of the caipi2’s equipment bays (that’s what they’re designed for), the adverse effect will most likely not be measurable and definitely not be noticeable under flight conditions, so practically there’s nothing really you’d even have to compensate for.

the most important part when building a medium-small wing like the caipi2 imho is to create a good mechanical basis for your flight controller to work with, most importantly a proper linkage geometry with good servo resolution, a tight fit and reasonable throws. the caipi2 is a great flier and, if setup correctly, will perform very well on ardupilot defaults.

grossly excessive control surface travel, failure to set the servo directions correctly and issues related to setting the arming parameters away from default imho are the most frequent plane-specific setup issues reported here.

cheers, basti


Thank you again @vierfuffzig for the amazing explanation. I will move forward with confidence (thanks to you) with leaving the offset defaults for the FC. I completely agree on the other items that will require more attention than the offset which are the elevon throws, avoiding slop in the control surfaces and just making sure the Caipi 2 is properly dialed in.

Thank you again for your assistance.
Cheers and happy flying!

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@Alexander_Perez did you ever get to tuning the gains? I have been searching to see if anyone had already posted some good initial gains to start with for the caipirinha.